(Host) Federal nuclear regulators have assured the state that a key safety system at the Vermont Yankee nuclear plant will not be weakened if it produces more power. The state had raised questions last year about the pumps needed to cool the reactor in an emergency.
VPR’s John Dillon reports:
(Dillon) Last December, Vermont’s nuclear engineer wrote a detailed letter to the Nuclear Regulatory Commission about safety issues raised by Yankee’s plans to increase power. Engineer Bill Sherman wanted assurance that pumps that are used to cool the reactor in an accident would have enough pressure to work.
Sherman pointed out that the pumps are less efficient at the hotter temperatures experienced at the higher power output. The NRC may allow Yankee to “take credit” for pressure in the reactor containment area as it calculates safety margins. That higher pressure is supposed to make sure that the emergency pumps work when they’re needed.
Here’s Sherman describing the issue before the state Nuclear Advisory Panel:
(Sherman) “That’s a new thing and we’re pretty skeptical about that. We’ve asked the NRC a number of very specific questions about a change in policy that they appeared to have made only in the last year or so. We’ve asked them for the basis of changing their policy. And we’ve asked for the safety implications of allowing credit for containment accident pressure.”
(Dillon) Late last month, the NRC finally responded to the state’s concerns. The federal agency says it’s reserving judgment on Yankee’s plan to produce more power. But it says that it’s allowed 27 other reactors to use the same method to calculate the safety of the pumps.
NRC spokesman Neil Sheehan said it’s extremely unlikely that the containment pressure would be needed to make the pumps work.
(Sheehan) “These calculations to begin with are very conservative. In other words, if you were just to look at an accident probability in a realistic way they wouldn’t have to take credit for this pressure after an accident. But the way we operate, we expect them to have very large margins of safety.”
(Dillon) But critics say the nuclear agency has violated one of the key principles of reactor safety. According to Paul Blanch, an engineer with 35 years of experience in the industry, the NRC in the past has always required multiple levels of redundancy in safety systems. Blanch says the concept is called “defense and depth.” He says the idea is that no single failure of a key system will allow an accident to escalate or radiation to be released.
(Blanch) “If the containment fails, and it only takes a leaky valve or a leaky penetration or an inadvertent operator action and they lose containment pressure then they lose the ability to the cool the core. And it could jeopardize the cladding of the reactor fuel. So they’re clearly violating the most basic safety requirements and philosophy that this industry has been safely built upon for the last 40 or so years.”
(Dillon) Officials at the Public Service Department, the agency that represents ratepayers, say they’re still reviewing the NRC letter. The NRC has until next January to rule on the Yankee uprate.
For Vermont Public Radio, I’m John Dillon.